Copyright © 2007, 2008 AudioNote Kits
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Page 32
The Filament Board is divided into two sides - each side takes in an AC input voltage regulates it down to the a correct DC
filament voltage - The most typical configuration of the mono block is 300B single triode - In this particular case we have
one half of the filament board provide a 5v DC for the 300B tube and the other side provides a 6.3v DC for the 6SH7 tube.
The way that we can get different DC voltages is because we are using the LM1084 adjustable regulator that can be set
with external resistors to provide the desired voltage - For example in order to have a DC output voltage of 5v for the
300B we need to have a ratio of 3:1 between the resistor pair - For a 6.3v filament we need a 4:1 ratio so we use 91 and
360R.
The other important information to consider is that we use a 0-6.2-8.3 secondary winding off of the Mains transformer to
supply the AC voltage for each side of the filament board - For the 300B (5v) and the 6SH7(6.3v) we use the 0 & 8.3v taps
as inputs to the filament board. This AC voltage is then regulated down to the 5v or 6.3v via the LM1084 regulator. For
2A3 where we only need 2.5v DC output we use the 0 & 6.2v AC input taps. You can use this information when you are
checking over your wiring - If you have any questions feel free to contact us!
Start by installing the KBU6J Bridge
Rectifiers.
You will need to bend the legs slightly
to install in board.
Note that the slanted edge of the
rectifier is towards the front of the
board – see next picture.
Here you see the correct height of the rectifier and the position of the front.
Install the second Bridge Rectifier into the BR2 position in the same manner.
We are now going to install the four large polarized
electrolytic capacitors.
You will notice the bar on one side of the capacitor – this is
the negative side (-). The shorter lead is also on the (-)
side.
The PCB will be marked with a + to show the correct
orientation.
These capacitors must be inserted the correct way around.
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